Impact of substrate sulphide passivation on photoluminescent properties of InAs autoepitaxial layers

Photoluminescent properties of indium arsenide autoepitaxial layers have been investigated by low-temperature Fourier-transform infrared spectroscopy. The structures were grown by hydride vapour-phase epitaxy on heavily doped n + -InAs substrates. Sulfide passivation of the substrates was carried out in a unimolar aqueous solution of sodium sulfide at room temperature, which leads to the removal of the natural oxide layer and the formation of a sulfur layer protecting the substrate surface. Three distinct peaks were detected in the photoluminescence spectra of the structures measured on a Fourier-transform infrared spectrometer at 8 K. The peak with an energy of 415 meV corresponds to the direct interband transition in indium arsenide. The power dependence of the second peak, with an energy of 400 meV, has a sublinear character, which allowed us to attribute it to the emission of bound excitons. A structure with a series of closely spaced peaks was observed in the PL line of the third peak with a maximum at an energy of 388 meV, which allows us to attribute this signal to the emission of donor-acceptor pairs. The effect of substrate sulfidisation on the quality of InAs epitaxial layers was assessed by comparing the relative area of the PL peak of bound excitons for sulfidised and non-sulfidised structures. It is shown that the decrease in the relative peak area of bound excitons after substrate sulfidisation is due to a decrease in the number of defects in the InAs autoepitaxial layers.